Aircraft doors of many passenger aircraft are provided with an evacuation slide which can be selectively deployed in the case of an emergency landing in order to allow passengers to quickly leave the aircraft through the respective door. The deployment of such slides is controlled by slide actuation means, which are part of or controlled by a local door controller, which is associated with the door and adapted to control various functions thereof. Typically, the slides have an activated state and a deactivated state between which they can be switched by a slide release lever. In the activated state the slides are automatically deployed upon opening of the respective door, whereas in the deactivated state the door can be opened without causing deployment of the slide.
Such an evacuation slide is normally in a retracted state, in which the slide is integrated into the door. When deployed the slide projects from the door and extends in an oblique manner from the door opening towards the ground. In order to enable passengers to safely reach the ground when using the slide the deployed slide must be long enough to reach the ground.
In this regard it must be taken into consideration that after an emergency landing the aircraft may be damaged and may therefore possibly not be in its normal landing position, in which the longitudinal axis of the aircraft is extending horizontally, i.e., parallel to the ground. Such non-horizontal orientation of the aircraft may also occur if some of the wheels of the aircraft come to rest on an unevenness. Thus, at the time at which an evacuation slide of the aircraft is to be used, the aircraft may be in a position in which the longitudinal axis of the aircraft is inclined with respect to the ground for the above reasons. This has the consequence that the actual distance between an aircraft door, at which an evacuation slide is to be deployed, and the ground may be larger than in the case of the normal horizontal orientation of the aircraft. For example, the aircraft may be, in particular, in a nose-up position, in which the nose of the aircraft is pointing upwardly in an oblique manner, because the nose wheel is in the air spaced from the ground. In such a nose-up position the distance between the front aircraft doors, which are typically provided with evacuation slides, and the ground is larger than for the normal horizontal orientation, in which all wheels are in contact with the ground. In these cases an evacuation slide, which is configured for the case of the normal horizontal orientation of the aircraft, either does not reach the ground at all or extends at an angle which is too steep to allow for a safe use of the slide.
For this reason it is known to construct evacuation slides such that they can be selectively deployed with two different lengths, a normal length corresponding to a horizontal orientation of the aircraft and an increased length corresponding to an orientation of the aircraft in which the pitch angle with respect to the horizontal direction exceeds a defined limit value. For example, the slide may comprise a main portion and an extension portion, wherein the main portion can be deployed either alone or together with the extension portion. Such an evacuation slide is able to address, in particular, the above-mentioned nose-up situations. In order to enable the determination of the pitch angle required for this purpose, the aircraft comprises a plurality of pitch angle sensors, which are installed at a central location in the aircraft and are connected by cables to the door controllers or a slide release means of individual doors.
In this manner, the door controllers or slide release mechanisms connected to the pitch angle sensors are able to take into consideration the current pitch angle when deploying the slide and to control the deployment length of the slide accordingly.
In order to be able to account for situations in which an evacuation slide fails to deploy either partially or completely the associated door controller may be configured to receive a signal from the slide which is indicative of deployment of the slide and of the actual deployment length of the slide, e.g., of the number of deployed stages of a multi-stage slide. Such signal may be generated by suitable sensors provided on the slide. Based on the signal the door controller is able to detect a failure of the slide and to control a signaling device associated with the door to provide an indication that the slide is not ready for use. For example, the signaling means may be an optical signaling means or an acoustic signaling means, so that the indication may be optical or acoustical.
For the purpose of providing this indication and also in order to also account for situations in which the pitch angle of the aircraft changes after deployment of the evacuation slide at the beginning of an evacuation, the door controller is typically configured to monitor and analyze for a predetermined minimum time period of, e.g., 120 seconds after initiating deployment of the slide the signal from the slide and the pitch angle and to determine whether the actual deployment length of the slide is large enough for the particular door and for the current pitch angle of the aircraft. When it is determined that the deployment length is not large enough, the indicating means is controlled to indicate that the slide is not ready for use.
This arrangement is not very flexible and requires high installation and maintenance effort. For example, it requires high effort to manually calibrate the pitch angle sensors. Further, all door controllers need to implement the functionality for monitoring and analyzing the pitch angle and the deployment length of an evacuation slide after deployment thereof, even though this functionality is typically only required at the two doors nearest to the nose, because specifically for these doors nose-up situations pose a problem. This functionality unnecessarily adds to the costs and weight of the door controllers.